Conventionally, for example, a structure shown in FIG. 5 is known as a terminal structure of a superconducting cable (see Patent Document 1). This terminal structure includes a terminal of a superconducting cable 100, a refrigerant bath 101 housing this terminal, a bushing 102 providing electrical conduction from a superconducting conductor 100a of cable 100 to a room-temperature side, a vacuum container 103 covering an outer periphery of refrigerant bath 101, a porcelain tube 104 protruding from a room-temperature side of vacuum container 103.
Bushing 102 has in its center a conductor 102a which is electrically connected to superconducting conductor 100a via a joint 105 and which is covered with a solid insulator 102b such as ethylene propylene rubber therearound, and is housed along from vacuum container 103 to porcelain tube 104. It is noted that, in the example shown in FIG. 5, stress cones 102c are arranged on an outer periphery of solid insulator 102b in the vicinity of both ends of bushing 102, respectively.
Porcelain tube 104 is filled with an insulating fluid 104a such as an insulating oil and SF6 gas. Refrigerant bath 101 includes a liquid refrigerant layer 101b filled with a liquid refrigerant 101a such as liquid nitrogen supplied from a supply pipe 106 and a gaseous refrigerant layer 101d filled with a refrigerant gas 101c such as helium gas and nitrogen gas in a layer on liquid refrigerant layer 101b in FIG. 5. Refrigerant gas 101c can be discharged through a discharge pipe 107. Refrigerant gas 101c is also maintained in a state pressurized by a pressurizer (not shown) so that liquid refrigerant 101a may not rise to the room-temperature side.
Vacuum container 103 in a cryogenic side and porcelain tube 104 in the room-temperature side are separated by a flange 108. This flange 108 is usually provided with a seal 109 to keep airtightness in order to prevent refrigerant gas 101c of gaseous refrigerant layer 101d from entering porcelain tube 104 in the room-temperature side.
Patent Document 1: Japanese Patent Laying-Open No. 2002-238144 (FIG. 3)